Microstructure engineering of fusion zone in resistance spot welding of martensitic stainless steels: The role of Ni interlayer thickness

Transitioning solidification mode via electroplated Ni coatings in martensitic stainless steel resistance spot welds: new insights into fabricating tough microstructure

“…It has also been shown that the in-situ post-weld heat treatment through the martensite tempering mechanism improves the mechanical properties in tensile-shear (TS); however, the cross-tension (CT) properties did not improve much and just barely met the minimum standard strength criteria 11 , 12 . Conversely, the utilization of a nickel interlayer has demonstrated substantial improvement in both the TS and CT mechanical properties of AISI420 MSSs by the authors of this study 9 , 13 , surpassing minimum strength requirements by a considerable margin. It is worth mentioning that various interlayers have been examined for purposes beyond enhancing weld nugget toughness, e.g.…”

“…Different pathways have been explored in literature to enhance the weldability of MSSs, including strategies like enlarging weld nugget size 8 , 10 , in-situ tempering of weld nugget 11 , 12 , and employing Ni interlayer 9 , 13 . Attempts to enlarge WN size by increasing the welding current have revealed limited impact on the microstructure.…”

“…Notably, introducing a 0.5 mm thick Ni interlayer between 1.5 mm MSSs led to a notable modification in the chemical composition of WN, resulting in a remarkably tough austenitic microstructure in the WN 9 , a concept that has since been adopted by subsequent research studies 21 , 22 to enhance the weldability of steels. Additionally, the thickness of the Ni interlayer has been identified as a critical factor influencing the phase transformations of the WN 13 . In a recent study 13 , the same research group focused on designing an engineered microstructure to enhance the weldability of MSSs in the automotive industry.…”

“…Additionally, the thickness of the Ni interlayer has been identified as a critical factor influencing the phase transformations of the WN 13 . In a recent study 13 , the same research group focused on designing an engineered microstructure to enhance the weldability of MSSs in the automotive industry. This was achieved by strategically controlling the solidification mode within the WN by inserting various thicknesses of Ni interlayer between MSS base metals.…”

“…In the best-case scenario, the CT and TS strength were about 4 times and twice higher than conventional MSS spot welds, respectively, making these welds highly reliable. That idea was able to improve weldability of MSSs more efficiently than the other approaches such as in-situ rapid tempering or simply increasing WN diameter 11 – 13 . Although there are limitations to implementing Ni interlayer within the automotive industry, the study provided a systematic guideline for selecting a critical interlayer thickness for spot welding of steels.…”